—Must I return the book this week?— No you . You can it for 20 days.A. mustnt: keep B.

问题补充：

—Must I return the book this week?

— No, you . You can it for 20 days.

A. mustn : keep

B. needn ; borrow

C. needn ; keep

D. mustn ; borrow

答案：

A. mustn : keep

B. needn ; borrow

(答案→)C. needn ; keep

D. mustn ; borrow

解析：mustn 禁止，一定不；needn 不必；keep持有，保存；borrow借来。句意：我必须这周归还这本书吗？——不，你不必。你可以持有20天。结合语境可知选C。